The present invention relates to polyfunctional proteases, and more particularly to polyfunctional proteases as novel intracellular proteases.
The polyfunctional protease, which is locally present in the cytoplasm as an inactive protease, was separated from the rat livers by the present inventor and its functions, molecular structure, distribution, locality, etc were reported (The Journal of Biological Chemistry, 261(32), pp 15197-15203; 1986 ibid. pp 15204-152-7 (1986); Kagaku to Seibutsu 25(8), pp 489-490 (1987); Tanpakushitsu Kakusan Kouso 32(7), pp 955-961 (1987); etc. ).
The above protease is believed to have a molecular weight of about 750,000, which is exceptionally large for a protease. The protease is a giant protein complex in the form of heteropolymer and has in one molecule a plurality of catalytic sites which are different in substrate specificity and independent of one another. For this reason the protease is referred to as a "polyfunctional protease". When observed through a electron microscope, the molecule of this enzyme is found to be of an annular particle structure. Therefore, the protease is also referred to as "proteasome"(Nature, 331, 192-194 (1988) This protease is believed to be an enzyme in a non-lysosomal proteolytic pathway.